Strong consumer interest in home satellite TV reception has instigated research by electronics manufacturers for better performing, more cost-effective, TVRO earth station terminals. A TVRO terminal is the down-link system in a typical satellite television system which includes four major components: a television studio for generating TV signals, an up-link earth station for communicating the TV signals into space, a geostationary communication satellite for receiving the TV signals and for retransmission of the signals to the earth, and the TVRO for receiving and converting the signals into audio and video displays.
The TVRO earth station terminal includes six major components: a directional dish receiving antenna, a low noise preamplifier (LNA), a frequency down converter, a satellite TV receiver, a VHF remodulator, and a conventional television set.
Satellite TV signals are transmitted on a frequency modulated signal, and as such the satellite TV receiver must include a detector responsive to frequency modulated transmissions. Experience with conventional television receivers has shown that quadrature, or coincidence, detectors are good detectors for frequency modulated signals.
With the advent of integrated circuits, several electronics manufacturers have provided quadrature detector integrated circuits. Heretofore, however, such integrated circuit chips have been in the most part limited in their application to the detection of frequency modulated signals carrying sound information. The applications have been so limited because the chips require an external tuned circuit to provide the phase shift essential for quadrature detection. In order to accommodate the broad bandwidth required of an FM signal carrying video information, the shunt resistance of the tuned circuit must be decreased, to broaden the responsive bandwidth of the tuned circuit. At the same time, however, the decrease in shunt resistance of the tuned circuit lowers the output power of the detector, and detracts from the selectivity of the circuit.
A quadrature detector circuit that could incorporate standard integrated circuit chips, and that could detect across a bandwidth suitable for demodulating video information on a frequency modulated carrier wave, without decreasing the power out of the detector or reducing its linearity, would be a decided advantage.